The invention relates to pigment-containing oil-based gel materials, colored pencils containing them and a process for the production of colored pencils.
Pigment-containing oil-based gel materials are dispersed systems which consist of a skeleton of the gel-forming component with an oil component incorporated therein. The gel material furthermore contains pigments for coloring. Such materials are suitable for applying colors in many areas. Suitable principal fields of use for pigmented gel materials are in colored materials for drawing and painting and the area of decorative cosmetics, where they can be used in many forms, inter alia for make-up, creamy eye shadows, lipsticks and eyeliner and eyebrow pencils. In particular, such pigment-containing gel materials can be used for producing cosmetic pencils or sticks.
Materials used for drawing, painting or make-up should be capable of being easily applied but should be well retained after application and should as far as possible be water-resistant, in the case of cosmetics pencils also tear-resistant, and transfer-resistant, i.e. should not stain other surfaces and articles and should not bleed from the area of application.
Known formulations for pencils or sticks are based on a mixture of waxes and oils which is colored with pigments. Thus, pencil or stick formulations composed of natural or mineral waxes, natural or synthetic oils or mineral oils and conventional additives, such as lanolin or lanolin derivatives, are described, for example, for lipsticks or eye shadow pencils. As a rule, these formulations are thixotropic systems which liquefy under the shear forces occurring during application and thus permit gentle application.
In the area of cosmetics, gel-like mixtures have predominantly been used to date for deodorant and antiperspirant sticks. They contain a considerable proportion of volatile silicone oils, such as cyclomethicone or dimethicone, or hydrocarbon oils, such as isoparaffin. These gels have the advantage that they can be readily applied but the disadvantage that they have no mechanical load capacity. For deodorant sticks, the advantage of easy application predominates whereas, owing to the shape of the sticks, stability is not so important. Deodorant sticks have a large diameter in relation to their length and the requirements with respect to the strength are not very high owing to the composition of the sticks. It has been found that materials which are suitable as deodorant sticks can be shaped into relatively thin leads only to a limited extent and in particular, since the material is too soft and unstructured, can be removed from the mold only with great difficulties or not at all.
Attempts have also been made to prepare oleogels containing candelilla wax and to shape them into leads. Owing to its gloss, candelilla wax is popular for lipsticks and eye shadow pencils. However, it has been found that the known oleogels have an insufficient oil-binding capacity, so that phase separation occurs and the oil contained in the material migrates into the environment. This impairs the aesthetic appearance of the pencil. Moreover, the loss of oil results in the sticks losing their elasticity and becoming brittle. In addition, it has been found that, as a result of the diffusion, evaporation or migration of the oil, the leads produced from the material shrink to such an extent that, when an attempt is made to produce colored pencils, leads inserted into wood slip out of the wood sleeves after a short time.
It is an object of the present invention to eliminate the disadvantages described above and to provide an oil-based gel material which has a high oil-binding capacity and which is suitable for being processed to give leads for pencils, in particular cosmetic pencils. It is a further an object of the invention to provide a material whose texture is stable and which as far as possible is water- and tear-resistant and is transfer-resistant, i.e. does not stain surfaces or articles after application. In addition, the application properties of the material should be good, i.e. it should be capable of being applied up to about 40.degree. C. without deforming or smearing but should also not be too hard. For cosmetics pencils, it is moreover desirable for the gel material to be composed of only a few, cosmetically acceptable components. Moreover, the material should be capable of being shaped by casting or extrusion.